Controller for electric automobile

ABSTRACT

A control device of an electric car in which any two of control devices fixed to the corresponding electric motors send signals to each other and send and receive control information by taking a bypass route when any one of transmission lines malfunctions is provided. 
     Fail safe means for signal transmission lines, in which a bypass route is established such that a node detecting a communication failure in an electronic control system of the car sends a search message for searching a transmission route and another node which is able to establish the transmission route sends back a response message, is provided.

TECHNICAL FIELD

The present invention relates to a control device of an electric carhaving fail-safe means in its electronic control system.

BACKGROUND ART

There is an urgent need to develop a totally electric car as one ofdecisive factors in preventing air pollution due to motorization. Withthe understanding that conservation of the natural environment is a bigissue in the 21st century, the inventor of the present invention startedthe development in 1980s and is now yielding results.

As shown in FIG. 1, an electric car is driven by using only a drivingforce of an electric motor 101. When a secondary battery, an enginegenerator, or a fuel battery is used as a power source for the electricmotor 101, the electric car is respectively referred to as an electriccar A in the narrow sense, a series hybrid car B, or a fuel battery carC. The reference numerals 102, 103, 104, 201, 202, 301, and 302respectively denote a wheel, a controller, a secondary battery, anengine, a generator, a hydrogen feeding source, and a fuel battery.

As mentioned above, since the electric car is driven by using only adriving force of a rotary electric motor, it is defined as a car whichuses a secondary battery, a fuel battery, a generator using aninternal-combustion engine, a solar battery, or the like, or acombination of at least two of them, as a power source for the electricmotor. Although the electric car uses only a secondary battery in thefollowing description, those skilled in the art will appreciate that thepresent invention is applicable to a car which uses a fuel battery, agenerator using an internal-combustion engine, or a solar battery as apower source.

In order to improve the safety and the ease of use of a car in driving,an electronic system essential for the safety of the car has beenincreasingly equipped with redundant components such as sensors andcomputing elements.

In a disclosed example, position sensors of an operating member whichcan be operated by a driver, sensors for detecting the number ofrevolutions, or the like are redundantly provided. A signal from ameasuring device having such a redundant structure is fed to twoprocessors, each controlling a driving output of a car in accordancewith substantially the same computer program as that of the other.Output signals from the two processors act on a common variable whichaffects an output of a driving unit.

However, if this type of system is made fully redundant, it becomes verycomplicated, resulting in an increased cost and an increased frequencyof failures.

As is well known, a present car is equipped with a plurality ofelectronic control units, in particular, including a speed control unitand a steering control unit. Each of these control units acts on anothervariable of a driving unit of the car.

In the present car, these control units are mutually connected to eachother by an electronic connecting system and mutually exchange data andinformation therethrough.

Although a speed control of the electric car is performed by feeding anelectrical signal from an accelerator pedal to a control device forcontrolling an electric current to be applied to its electric motor,when a plurality of electric motors are used to drive the car and alsowhen an acceleration, a deceleration, and a turning angle of the car arecontrolled, an additional central control device for controlling theoverall car is required. In such control devices, the central controldevice and each of the control devices fixed to the correspondingelectric motors have been connected by a corresponding signal line so asto perform a control.

DISCLOSURE OF INVENTION

However, in such a control method, when one of transmission linesmalfunctions, it becomes impossible to control a corresponding electricmotor.

In view of the above-mentioned circumstances, an object of the presentinvention is to provide a control device of an electric car in which anytwo of control devices fixed to the corresponding electric motors sendsignals to each other and send and receive control information by takinga bypass route when any one of transmission lines malfunctions.

In order to achieve the above object,

[1] the present invention provides a control device of an electric carincluding a plurality of driving wheels, each having a drive motor fixedthereto, which includes a plurality of speed control devices, each fixedto the corresponding drive motor for accelerating or decelerating thecorresponding drive wheel in accordance with an external electricalsignal, and which includes a main control device having functions ofsending a control signal, to each of the speed control devices, forperforming an acceleration or deceleration in accordance with a commandfrom a driver or at least one of on-board sensors, and also receiving acontrol signal including information of an operating state of each ofthe drive motors and the speed control devices.

[2] In the control device of an electric car set forth in the above [1],a voltage of a battery, a current fed from the battery, and a batterytemperature are included as sensor signals which are input into the maincontrol device.

[3] In the control device of an electric car set forth in the above [1],a steering-angle of a steering wheel is included as a sensor signalwhich is input into the main control device.

[4] In the control device of an electric car set forth in the above [1],a signal indicating that a battery is being recharged from a batterycharger is included as a sensor signal which is input into the maincontrol device.

[5] In the control device of an electric car set forth in the above [1],signals representing a brake command value from a brake controller and ahydraulic pressure of a master cylinder are included as sensor signalswhich are input into the main control device.

[6] In the control device of an electric car set forth in the above [1],a steering-angle signal of a steering wheel is included as a controlsignal sent from the main control device.

[7] Also, the present invention provides a control device of an electriccar, which includes fail safe means for signal transmission lines,wherein a bypass route is established such that a node detecting acommunication failure in an electronic control system of the car sends asearch message for searching a transmission route and another node whichis able to establish the transmission route sends back a responsemessage.

[8] In the control device of an electric car set forth in the above [7],each of the nodes includes self-node-ID storing means for storing itsown node identifier, adjacent-node-ID storing means for storingidentifiers of adjacent nodes connected to the transmission route, andprocessing means for processing route setting on the basis of a messagesent to the node. [9] In the control device of an electric car set forthin the above [8], the node is provided at each of a car controller andmotor controllers, each provided at a pair of driving wheels.

[10] In the control device of an electric car set forth in the above[8], the node is provided at each of a battery controller, a steeringcontroller, a brake controller, and a battery charging controller.

[11] In the control device of an electric car set forth in the above[9], the car controller and the motor controllers, each provided at apair of driving wheels, control corresponding power converters inaccordance with control signals received via the corresponding nodes.

[12] In the control device of an electric car set forth in the above [9]or [10], the bypass route is established by a control-signal-use,alternative main transmission line forming a closed loop and alternativetransmission lines connecting the alternative main transmission line andthe motor controllers.

[13] In the control device of an electric car set forth in the above[12], when a certain node detects that all communication lines andbypass routes to the car controller malfunction, the node stops anoperation of the corresponding motor controller, and the car controllerdetects that there is no response from the certain node and henceseparates the motor controller of the certain node from its controlobjects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the basic structure of an electrically powered car.

FIG. 2 illustrates a system configuration of an electric car accordingto an embodiment of the present invention.

FIG. 3 is a block diagram of an electronic control system of theelectric car according to the embodiment of the present invention.

FIG. 4 is a flowchart illustrating the steps of detecting a vehiclespeed according to the embodiment of the present invention.

FIG. 5 is a flowchart illustrating the steps of a target-yaw-rate(target-slip-angle) adaptive control according to the embodiment of thepresent invention.

FIG. 6 is a flowchart illustrating the steps of a TRC/ABS equivalentcontrol according to the embodiment of the present invention.

FIG. 7 is a flowchart illustrating an operation sequence of a carcontroller according to the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A control device according to an embodiment of the present inventionwill be described with reference to the accompanying drawings. Thecontrol device controlling individual motors so as to improve therunning stability of the vehicle under slipping is equipped with a failsafe mechanism and is mounted on an example electric car having a wheelconfiguration system in which each pair of two wheels are suspended by atandem wheel suspension and having six or more drive wheels, each wheelformed so as to be equipped with an in-wheel drive system.

Since the present invention is characterized by fail safe means in acontrol system including an electronic control unit, other controlsystems and devices are applied if needed.

(1) System Configuration

FIG. 2 illustrates a system configuration of an electric car accordingto an embodiment of the present invention.

In the present invention, a wheel system in which all pairs of two frontand rear wheels are suspended by a tandem wheel suspension is not alwaysrequired, and another wheel system in which only two pairs of front orrear wheels are suspended by the corresponding tandem wheel suspensionmay be used.

The electric car according to this embodiment is of an in-wheel-motor,eight-wheel-drive type. That is, the electric car has a wheel systemsuspended by the tandem wheel suspension and has an in-wheel drivesystem in which all wheels have respective motors incorporated therein.

Since this configuration allows each wheel to bear a reduced load, a TRCor ABS control is performed so as to be commensurate with the reductionin load, whereby a risk of slipping or the like can be reduced and therunning stability can be improved.

Each motor can be driven by one of a variety of power sources whichfeed, for example, an alternating current, a direct current, and a pulsecurrent, by using corresponding power converters, that is, an inverter,a converter, and a chopper, respectively.

The system configuration in which an alternating-current power sourceand inverters serving as power converters are used will be nowdescribed.

A car controller 1 equipped with a micro-computer receives detectioninformation from a variety of sensors; processes the information asneeded and outputs a control command to each of motor controllers 2, 3,4, and 5. The control command from the car controller 1 is output toeach of the motor controllers 2, 3, 4, and 5, a battery controller A, abattery charging controller B, a brake controller C, and a steeringcontroller 22 via transmission lines R1, R2, R3, R4, R5, R10, R11, R12,and R13, alternative transmission lines CR2, CR3, CR4, CR5, CR10, CR11,CR12, and CR13, and a control-signal-use, alternative main transmissionline CR.

Also, the car controller 1 is equipped with an electronic control unit(ECU) for controlling an output torque, the number of revolutions, and aspeed of each of motors 30, 31, 32, 33, 34, 35, 36, and 37; monitoringand controlling the status of each of on-board components; informing adriver of the status of the car; controlling the feeding of a battery,the charging of the battery, a brake, and a steering mechanism; andperforming other functions, and has a processing micro-program forperforming the foregoing functions. In addition, detected outputs ofrotating position sensors (speed sensors) (SM) 50, 51, 52, 53, 54, 55,56 and 57; a power sensor 9 for detecting a voltage and/or a current ofthe battery; a brake sensor 14 for detecting an operation of the brake;a steering-angle sensor 15 for detecting a steering angle of a steeringwheel; a shift position (SP) switch 16 for detecting a shift position ofa shift lever; an accelerator sensor 17 for detecting an opening of anaccelerator; temperature sensors 18 for detecting temperatures of thebattery, inverters, and the like; and malfunction-detecting sensors 19for detecting the fact that a voltage and/or a current of each inverterbecome smaller than a threshold and the like are input into the carcontroller 1.

The speed sensors (for example, resolvers) 50, 51, 52, 53, 54, 55, 56and 57 attached to the corresponding wheels generate signals (forexample, pulse signals at every fine angular positional displacement)representing wheel speeds VRFF, VRFR, VLFF, VLFR, VRRF, VRRR, VLRF, andVLRR of the corresponding wheels and feed them to the car controller 1.

The accelerator sensor 17, the brake sensor 14, and the shift positionswitch 16 output signals respectively representing the depressed amountof a accelerator pedal (not shown), the depressed amount of a brakepedal 20, and a throwing range of the shift lever (not shown) (and ashift lever position in a range of engine-braking or the like), that is,a shift position. The steering-angle sensor 15 outputs a signal such asa steering angle δt, representing the detected result of a steeringangle of the steering wheel. The power sensor 9 of the battery 6measures and outputs a voltage and/or a current of the battery 6. Eachtemperature sensor 18 measures and outputs a temperature of equipmentsuch as an inverter. Each malfunction-detecting sensor 19 outputs amalfunction signal when a voltage and/or a current of each converterbecome equal to or smaller than a threshold.

When being input into the car controller 1, each of outputs of thesesensors is converted into data in a processable format by the carcontroller 1. Using the converted data, the car controller 1 decidescommand values of a torque, the number of revolutions, a vehicle speed,and so forth, changes over a control method, and performs others. Asystem configuration for performing a torque control will be nowdescribed by way of example.

The motor controllers 2, 3, 4, and 5 equipped with respectivemicro-computers receive control commands from the car controller 1 viathe transmission lines, process the control commands as needed, andoutput the processed control commands to corresponding pairs ofinverters 10 and 10′, 11 and 11′, 12 and 12′, and 13 and 13′. Inaccordance with torque command values TRF, TLF, TRR, and TLR, the motorcontrollers 2, 3, 4, and 5 control the corresponding pairs of inverters10 and 10′, 11 and 11′, 12 and 12′, and 13 and 13′ so as to performtorque controls of corresponding pairs of motors 30 and 31, 32 and 33,34 and 35, and 36 and 37. All the torque command values provided to themotor controllers 2, 3, 4, and 5 are output from the car controller 1.Each of the inverters 10, 10′, 11, 11′, 12, 12′, 13, and 13′,respectively, for the motors 30, 31, 32, 33, 34, 35, 36, and 37 iscontrolled on the basis of detected phase currents of the correspondingmotor obtained from current sensors (not shown) or on the basis ofestimated phase currents of the corresponding motor computed from anangular position of its rotor or the like.

The wheel system suspended by the tandem wheel suspension includes aright-front front-wheel RFF40, a right-front rear-wheel RFR41, aleft-front front-wheel LFF42, a left-front rear-wheel LFR43, aright-rear front-wheel RRF44, a right-rear rear-wheel RRR45, a left-rearfront-wheel LRF46, and a left-rear rear-wheel LRR47 having the motors30, 31, 32, 33, 34, 35, 36, and 37 respectively incorporated thereinto.

The battery 6 serves as a driving power source to each motor, and itsoutput is fed to the motors 30 and 31 via the inverters 10 and 10′, themotors 32 and 33 via the inverters 11 and 11′, the motors 34 and 35 viathe inverters 12 and 12′, the motors 36 and 37 via the inverters 13 and13′, respectively. Under the control of the motor controller 2controlled by the car controller 1, the inverters 10 and 10′0 convertthe output power of the battery 6 (in this figure, into a power ofthree-phase alternating current) and feed it to the corresponding motors30 and 31 in order to control their torques, speeds, and so forth. Theinverters 11, 11′, 12, 12′, 13, and 13′ operate likewise.

A brake system for putting brake on each of front and rear, right andleft tandem wheels with both hydraulic and a regenerating brakes is usedin FIG. 2 under the design policy of maintaining the safety of the car.

More particularly, when the brake pedal 20 is depressed, a hydraulicpressure generated in a master cylinder 21 in accordance with the abovedepression acts on brake wheels BW60, BW61, BW62, BW63, BW64, BW65,BW66, and BW67 via respective wheel cylinders fixed to the correspondingwheels so as to provide brake torques to the wheels.

On the other hand, a detection signal in accordance with a brake force(a hydraulic pressure of the master cylinder 21) FB detected by thebrake sensor 14 is input into the car controller 1 over the transmissionline R12 via a node N12, and the car controller 1 generates the torquecommand values TRF, TLF, TRR, and TLR for performing the regeneratingbrake in accordance with the foregoing detection signal. A command valuein accordance with the control command such as a torque command value ora speed command value serves as a regeneration command value.

Accordingly, a brake force distribution in the car shown in FIG. 2increases in both the hydraulic brake and the regenerating brake as thebrake force FB increases. As mentioned above, since a hydraulic systemand a regeneration system are separated down from the brake sensor 14and are also backed up by the transmission lines, even when any one ofthe hydraulic and regenerating brakes malfunctions, the other can savethe car.

In addition, since a hydraulic pump used for a TRC/ABS control is notinstalled in the hydraulic system and only a proportioning valve formaking the front and rear distribution of the hydraulic brake forceproper is installed, the structure of a hydraulic brake system becomessimple. One of the reasons for eliminating the hydraulic pump and thehydraulic device for performing the TRC/ABS control from the hydraulicsystem is the configuration of this embodiment characterized in that therunning stability of the vehicle is controlled by utilizing controls ofoutput torques of motors.

The fail safe mechanism characterized by this invention includes thecontrol-signal-use, alternative main transmission line CR forming aclosed loop; the alternative transmission lines CR2, CR3, CR4, CR5,CR10, CR11, CR12, and CR13 for connecting from the alternative maintransmission line CR, respectively, to the motor controllers 2, 3, 4,and 5, the battery controller A, the battery charging controller B, thebrake controller C, and the steering controller 22; the motorcontrollers 2, 3, 4, and 5; the battery controller A; the batterycharging controller B; the brake controller C; the steering controller22; the car controller 1 for performing an overall control; and thetransmission lines for connecting each of the motor controllers, thebattery controller A, the battery charging controller B, the brakecontroller C, and the steering controller 22 to the car controller 1.

(2) Basic Control of Car

FIG. 7 is a flowchart of an operation sequence of the car controlleraccording to the embodiment of the present invention.

First, the car controller 1 detects a vehicle speed VS (Step S1).

Although a variety of sequences for detecting the vehicle speed VS canbe employed, an example sequence shown in FIG. 4 is preferably employed.In the following description, a sequence for detecting the vehicle speedVS is shown by a flowchart shown in FIG. 4. In this figure, the carcontroller 1 reads detected values V of the wheel speed sensors (SM) fora pair of two tandem-structured wheels (Step S30), and computes wheelangular-accelerations dω/dt (Step S31). The following expression can beused for computing a wheel angular-acceleration:dω/dt←(1/R)×dV/dtwhere R is a radius of a wheel, and V and ω is respectively a wheelspeed and a wheel angular-velocity of the wheel whose angularacceleration is to be computed.

The car controller 1 compares the absolute values of the above-computedwheel angular-accelerations dω/dt of the foregoing one pair with apredetermined threshold. When the absolute values of the pair of twowheels (i.e., all two wheels) exceed the predetermined threshold, thecar controller 1 determines that a slip (SL) occurs; when the absolutevalue of one of the pair of wheels exceeds the threshold and that of theother wheel does not exceed it, the car controller 1 determines that noslip (SX) occurs and also holds the wheel speed V of the other wheel asa wheel speed of the pair; and when the absolute values of the wheelangular-accelerations dω/dt of the pair of two wheels (i.e., all twowheels) do not exceed the predetermined threshold, the car controller 1determines that no slip (SX) occurs and also holds the larger one of thewheel speeds as a wheel speed of the pair (Step S32).

When the car controller 1 determines that no slip (SX) occurs at thepair of wheels, the wheel speed V of the wheels is added to a variableVS (Step S33). Meanwhile, when the car controller 1 determines that aslip occurs at the pair of wheels, since it is considered that a slipoccurs or is likely to occur because the absolute values of the angularaccelerations dω/dt exceed the predetermined threshold, a variable NSfor counting the number of pairs of wheels which are considered to slipor to be likely to slip (slipping wheels) is incremented by 1 (StepS34).

Upon carrying out Step S33 or S34, the car controller 1 stores thelocation and the wheel speed V of the pair of wheels in a memory or thelike (Step S35). The car controller 1 applies the sequence from Step S31to S35 to all drive wheels including all tandem-structured wheels (StepS36).

Upon determining whether each pair of all drive wheels are slippingwheels or non-slipping wheels, the car controller 1 determines whetherthe number NS of pairs of slipping wheels is equal to 4 or not, that is,whether all drive wheels slip or not (Step S37). Since all drive wheelsdo not usually slip or are likely to slip at the same time, the carcontroller 1 computes the vehicle speed VS by dividing the value VSaccumulated in repeatedly carried out Step S33 by (4−NS), that is, thenumber of pairs of non-slipping wheels (Step S38).

Meanwhile, when the relationship NS=4 holds, the car controller 1searches which drive wheel has started lastly to slip by using theinformation stored when Step S35 was carried out (Step S39).

The car controller 1 sets the wheel speed V maintained by the drivewheel just before starting to slip, which was found by the above search,that is, which has started lastly to slip, as the vehicle speed VS (StepS40).

As described above, in this embodiment, the vehicle speed VS can berelatively accurately decided by computing the vehicle speed VS, inprinciple, only from the wheel speeds of non-slipping wheels, whereby atorque command value tentatively decided in a sequence, which will bementioned later, becomes proper. Also, with the tandem suspensionstructure, all the eight wheels rarely slip or are almost unlikely toslip. Even when the above-mentioned state happens, since the averagewheel speed maintained by the wheel, which has started lastly to slip,over a predetermined time period just before starting to slip is set asthe vehicle speed VS, relatively reliable information can be used fortentatively deciding the torque command value. Upon carrying out StepS38 or S40, the operation of the car controller 1 returns to Step S2shown in FIG. 7.

In FIG. 7, upon detecting the vehicle speed VS, in order to assess thesteering state, the car controller 1 first determines whether theabsolute value of the steering angle δt is equal to or greater than apredetermined threshold or not (Step S2). When the steering angleexceeds the threshold and no slip occurs (Step S12), the car controller1 performs a target-yaw-rate adaptive control or a target-slip-angleadaptive control (for example, a zero slip-angle control) (Step S3).

For example, when the absolute value of the steering angle δt detectedby the steering-angle sensor 15 is equal to or greater than thepredetermined threshold, that is, when it is determined that a driver issteering the car, the car controller 1 performs the target-yaw-rateadaptive control or the target-slip-angle adaptive control in order toprevent or suppress the driving instability of the vehicle caused by thesteering.

An example sequence of the target-yaw-rate adaptive control or thetarget-slip-angle adaptive control is shown in FIG. 5.

In a flow shown in FIG. 5, in accordance with an ON- or OFF-state of theaccelerator determined on the basis of an output of the acceleratorsensor 17, a shift position obtained by the shift position switch 16, asteering angle δt provided by the steering-angle sensor 15, dδt/dt whichcan be computed on the basis of the steering angle δt, and so forth, thecar controller 1 first selects a group of coupling coefficients (byusing an experimental expression) (Step S50).

Furthermore, the car controller 1 computes a wheel acceleration dV/dt ofeach wheel forming the tandem suspension structure and then computes acoefficient of road friction μ (by using another experimentalexpression) on the basis of the computed acceleration (Step S51). Thecar controller 1 decides a correction factor k of each wheel on thebasis of the coefficient of road friction μ and the steering angle δtand also by using the group of coupling coefficients selected in StepS50 (Step S52).

When the accelerator is in an ON-state (Step S53), the car controller 1tentatively decides a torque command value of each wheel, from apowering torque map, on the basis of its wheel speed V, an acceleratoropening VA, and the shift position (Step S54). Also, when theaccelerator is in an OFF-state (Step S53), the car controller 1tentatively decides a torque command value of each wheel, from aregenerating torque map, on the basis of its wheel speed V, the brakeforce FB, and the shift position (Step S55). The powering torque mapshows a characteristic of the number of revolutions vs. torque whereboth the torque and the number of revolutions are positive, and theregenerating torque map shows a characteristic of the number ofrevolutions vs. torque where the number of revolutions is positive andthe torque is negative. These torque maps are experimentally obtained inadvance.

The car controller 1 decides a torque command value by multiplying thetorque command value tentatively decided in Step S54, or S55 by thecorrection factor decided in Step S52 (Step S56) and outputs the decidedtorque command value to the corresponding motor controller (Step S57).

Accordingly, depending on methods for setting the group of couplingcoefficients which are selected in Step S50 and the correction factorsin Step S52, a torque command value in a range possible for performingthe target-yaw-rate adaptive control or the target-slip-angle adaptivecontrol can be in a regenerating region even when the accelerator is inan ON-state or can be in a powering region even when the accelerator isin an OFF-state. By performing the above-mentioned control, the runningstability of the vehicle in steering is improved in this embodiment.

Refer the disclosure in Japanese Unexamined Patent ApplicationPublication No. 10-210604 with regard to the target-yaw-rate adaptivecontrol and the target-slip-angle adaptive control. Meanwhile, a methodfor performing the running stability control by using a plurality ofstate variables which include a yaw rate acting on the vehicle and whichdemonstrate the moving state of the car instead of the target-yaw-rateadaptive control or the target-slip-angle adaptive control may beemployed.

Refer Japanese Unexamined Patent Application Publication No. 10-271613with regard to this method. Upon completing the target-yaw-rate adaptivecontrol or the target-slip-angle adaptive control, the operation of thecar controller 1 returns to FIG. 7.

The operation of the car controller 1 returns to Step S1 so as to repeatitself. In Step S2 which is performed upon detecting the vehicle speedVS, when it is admitted that there is no need for performing thetarget-yaw-rate adaptive control or the target-slip-angle adaptivecontrol, that is, when the absolute value of the steering angle is lessthan the threshold, in principle, the car controller 1 performs thesequence in association with an 8-WD control (Step S6).

When starting this 8-WD control Step S6, the car controller 1 firstperforms a determining and classifying process about the number NS ofpairs of slipping wheels, each pair corresponding to one pair ofslipping wheels forming the tandem suspension structure, detected in thesequence for detecting the vehicle speed VS.

In other words, when the number NS of pairs of the detected slippingwheels is equal to 4, that is, all the drive wheels slip or are likelyto slip (Step S7) or when the number NS of pairs of the slipping wheelsis 3, that is, when only one pair of the driving wheels forming thetandem suspension structure do not slip or are unlikely to slip (StepS8), the operation of the car controller 1 advances to a TRC/ABSequivalent control (Step S9), as opposed to advancing to the 8-WDcontrol (Step S6).

Also, even when the number NS of pairs of the slipping wheel is 2, inother words, even when two pairs of the drive wheels forming the tandemsuspension structure do not slip or are unlikely to slip (Step S10), theabove operation advances to the TRC/ABS equivalent control (Step S9)when both pairs of the detected slipping wheels lie together at the leftor at the right of the car (Step S11).

In addition, even when it is determined in the foregoing Step S2 thatperforming the target-yaw-rate adaptive control or the target-slip-angleadaptive control is likely necessary, the above operation advances alsoto the TRC/ABS equivalent control (Step S9) when the number NS of pairsof the slipping wheels is not zero, that is, when it is admitted thatany one pair of the drive wheels forming the tandem suspension structureslip or are likely to slip (Step S12).

An example sequence of the TRC/ABS equivalent control is shown in FIG.6.

In order to perform the TRC/ABS equivalent control, the car controller 1first selects groups of coupling coefficients and control constants, andthe like depending on whether the wheel speed V is high or low, whetherthe accelerator is in an ON-state or OFF-state, and so forth (Step S60).

The groups of coupling coefficients and control constants mentionedabove are respectively a group of coefficients used for deciding a groupof thresholds used for determining an angular acceleration, which willbe mentioned later, and a group of constants used for deciding afeedback torque. The car controller 1 tentatively decide a torquecommand value from the powering torque map in accordance with the wheelspeed V, the accelerator opening VA and the shift position when it isdetermined in Step S61 that the accelerator is in an ON-state (Step S62)and from the regenerating torque map in accordance with the wheel speedV, the brake force FB and the shift position when it is determined inStep S61 that the accelerator is in an OFF-state (Step S63).

Furthermore, when it is determined that the accelerator is in anON-state or OFF-state in Step S61, the car controller 1 decides thegroup of thresholds, respectively, on the basis of the acceleratoropening VA and the group of coupling coefficients selected in Step S60(Step S64) or on the basis of the brake force FB and the group ofcoupling coefficients selected in Step S60 (Step S65).

The car controller 1 classifies an angular acceleration dω/dt of eachwheel relative to the group of thresholds decided in Step S64 or S65(Step S66). The car controller 1 decides feedback torques by usingdifferent computing expressions or the like on the basis of theclassified results. For example, when the angular acceleration dω/dtlies in a first, second, third, - - - , or n-th range, the carcontroller 1 decides the feedback torque of each wheel by performing afeedback torque process with a first computing expression (Step S67-1),with a second computing expression (Step S67-2), with a third computingexpression (Step S67-3), - - - , or with a n-th computing expression(Step S67-n), respectively.

Moreover, constants of the computing expressions used in Steps S67-1,S67-2, S67-3, - - - , S67-n are given by the group of control constantsselected in Step S60. The car controller 1 decides torque command valuesby subtracting the corresponding feedback torques as decided above fromthe corresponding torque command values tentatively decided in Step S62or S63 (Step S68) and outputs the decided torque command values to thecorresponding motor controllers (Step S69).

Since a torque acting on each drive wheel can be varied if needed byusing the above-mentioned sequence, a function equivalent to the TRC/ABScontrol in a conventional engine-powered car can be achieved. Refer tothe disclosures in Japanese Unexamined Patent Application PublicationsNos. 8-182119 and 10-210604 with regard to the TRC/ABS equivalentcontrol. Upon completing the sequence shown in FIG. 6, the operation ofthe car controller 1 advances to Step S4 shown in FIG. 7.

When both the conditions for advancing to the target-yaw-rate adaptivecontrol or the target-slip-angle adaptive control and to the TRC/ABSequivalent control are not satisfied, in other words, when the absolutevalue of the steering angle δt is less than the corresponding threshold;when the number NS of pairs of slipping wheels forming the tandemsuspension structure is 2 or less; and when neither both wheels at theleft nor those at the right of the car are slipping wheels, the carcontroller 1 performs the sequence of the 8-WD control (Step S6).

In order to perform this sequence, the car controller 1 first determineswhether the number NS of pairs of the foregoing slipping wheels is 1 ornot (Step S13). Since the number NS is equal to zero when traveling onthe normal road, the operation of the car controller 1 advances to StepS14 and S15. In Step S14, the car controller 1 decides all drive wheelsforming the tandem suspension structure as distribution wheels. Thedistribution wheel mentioned here means a drive wheel to which a torqueoutput is actually distributed. In step S15, the car controller 1 setsdistribution ratios of a torque output to the corresponding distributionwheels at normal values. For example, a distribution ratio equal to 1 isset to all drive wheels. The foregoing distribution ratios may vary inaccordance with a load of the car or may be set at predetermined ratioswhich are different between front and rear wheels in accordance with thestructure of the vehicle.

Meanwhile, when it is determined that the number NS is equal to 1 inStep S13, or when it is determined that the conditions for advancing tothe TRC/ABS equivalent control are not satisfied in Step 11, the carcontroller 1 decides wheels other than the pairs of slipping wheels asthe distribution wheels (Step S16).

Furthermore, in order to prevent a yaw moment about the center ofgravity of the vehicle from acting on the vehicle when the torque isactually output, that is, in order to achieve a lateral balance of thevehicle, the car controller 1 adjusts a distribution ratio of each wheel(Step S17).

For example, the distribution ratio of a pair of the drive wheels whichare not selected as distribution wheels in Step S16, that is, a pair ofthe slipping wheels, is adjusted to be zero so as to prevent the pair ofwheels from being provided with torque command values, and thedistribution ratio of the pair of non-slipping wheels lying at eitherone of the right and left sides where the pair of slipping wheels lie isadded by the distribution ratio corresponding to the torque output whichwould otherwise be distributed to the pair of slipping wheels.

Upon performing Step S15 or S17, the car controller 1 tentativelydecides a torque command value from the powering torque map inaccordance with the vehicle speed VS, the accelerator opening VA, andthe shift position when the accelerator is in an ON-state (Step S19) andfrom the regenerating torque map in accordance with the vehicle speedVS, the break force FB, and the shift position when the accelerator isin an OFF-state (Step S20).

Upon performing Step S19 or S20, the car controller 1 adjusts the torquecommand value of each pair of wheels tentatively decided in Step S19 orS20 in accordance with the corresponding distribution ratio previouslyset or adjusted in Step S15 or S17 (for example, multiplying thetentatively decided value by the distribution ratio) so as to decide atorque command value of the pair of wheels (Step S21).

The car controller 1 outputs the torque command values decided in StepS21 to the corresponding motor controllers (Step S22), and then theoperation thereof advances to Step S4.

Accordingly, in this embodiment, the control state of the car is changedover in accordance with the slipping state of each wheel forming thetandem suspension structure. First, two wheels forming the tandemsuspension structure are regarded as one unit. When only one unit offour units of wheels slips, that is, when the relationship NS=1 holds,the torque command value which would otherwise be output to theseslipping wheels is output to the other drive wheels lying at the sameside as the slipping wheels. Likewise, when the relationship NS=2 holdsand also one unit of slipping wheels lies at each of the right and leftsides, a torque command value is output to a unit of non-slipping wheelsremaining at each of the right and left sides. In addition, when therelationship NS=2 holds and also both units of slipping wheels lie atthe left (or right) side, the TRC/ABS equivalent control is performed.Furthermore, when the relationship NS=3 or NS=4 holds, the TRC/ABSequivalent control is also performed. As described above, according tothis embodiment, since the car controller 1 changes over or varies acontrol mode of each motor output or a torque distribution ratio of eachwheel in accordance with the occurrence condition of slipping or theslipping tendency of the wheel, in particular, with the number of unitsof slipping wheels and the locations thereof, the 8-WD control and theTRC/ABS equivalent control suitable for use in an 8 wheel-drive electriccar of an in-wheel motor type are realized, and the running stability ofthe vehicle can be maintained and improved.

(3) Fail Safe Mechanism

Since the main electronic control unit is internally connected throughthe control-signal-use, alternative main transmission line CR asmentioned above, even when the transmission lines and the likemalfunction, the electric control unit backs up the control system,thereby performing necessary controls as usual.

A signal transmission system is formed by nodes (communication devices)installed at the car controller 1, the motor controllers 2, 3, 4, and 5,the battery controller A, the battery charging controller B, the brakecontroller C, and the steering controller 22, all forming the electroniccontrol unit as shown in FIG. 3. The nodes (communication devices) areformed by a plurality of nodes N1, N2, N3, N4, N5, N10, N11, N12, andN13 respectively having self-node-ID storing means N1 b, N2 b, N3 b, N4b, N5 b, N10 b, N11 b, N12 b, and N13 b for storing correspondingself-node identifiers N1, N2, N3, N4, N5, N10, N11, N12, and N13;adjacent-node-ID storing means N1 c, N2 c, N3 c, N4 c, N5 c, N10 c, N11c, N12 c, and N13 c for storing identifiers of corresponding adjacentnodes connected to the corresponding transmission lines and alternativetransmission lines; and processing means N1 a, N2 a, N3 a, N4 a, N5 a,N10 a, N11 a, N12 a, and N13 a for processing corresponding routesetting in accordance with messages sent to the corresponding nodes andare also formed by the transmission lines R1, R2, R3, R4, R5, R10, R11,R12, and R13, the alternative transmission lines CR2, CR3, CR4, CR5,CR10, CR11, CR12, and CR13, and the control-signal-use, alternative maintransmission line CR for connecting the above nodes so as to establishan bypass-route setting method by which a communication route is set soas to bypass a failed location.

According to the foregoing bypass-route setting method, when there is noresponse to the polling between adjacent nodes through the transmissionlines and the alternative transmission lines connected to thecorresponding nodes, it is regarded that a communication failure isdetected on the transmission lines or the alternative transmission linesbetween the two nodes; the node which detected the communication failuresends a search message s including its self-identifier and theidentifier of the adjacent node connected to the transmission lines onwhich the communication failure was detected; the node which receivedthe search message compares the identifier ID of the adjacent node inthe search message with identifiers stored in its self-node ID storingmeans and its adjacent node ID storing means; and, when all the abovecomparisons do not result in a coincidence with each other, the nodewhich received the search message relays the search message to othernodes, and when any one of the above comparisons results in acoincidence with each other, the node which received the search messagesends back a response message r for setting a bypass-route to the nodewhich detected the communication failure.

Data including a message type such as a search message or a responsemessage, an identifier (ID) of a receiving communication device, anidentifier (ID) of a sending communication device, an identifier (ID) ofa malfunction-related communication device, and a remaining linecapacity is written in a control section of a sending signal frame ofthe search message s or the response message r, respectively. Themalfunction-related communication device means a malfunctioningcommunication device or an adjacent communication device connected to amalfunctioning transmission line.

When each node detects that a transmission line between the node N1 ofthe car controller 1 and the node Nn of the corresponding motorcontroller is established, the node sets its own motor controller andinverter in a standby mode. Upon receiving a control command via thetransmission lines, the motor controller controls the correspondinginverter in accordance with the control command.

[Case (a)]

An example case where a communication failure B1 occurs on the signaltransmission line R2 between the car controller 1 and the motorcontroller 2 will be described with reference to FIGS. 2 and 3.

In accordance with the polling between the node N2 and the adjacent nodeN1 via the transmission line and the alternative transmission lineconnected thereto, the node N2 detects that a communication failureoccurs when no response comes from the opposing node. The processingmeans N2 a of the node N2 sends data, which includes information that amessage type is a search message s, an identifier of the sendingcommunication device is N2, and an identifier of the malfunction-relatedcommunication device is N1 and which is written in a control section ofthe corresponding signal frame, to the node N13 or N3.

(a-1) The setting of a bypass route via the node N3 will be firstdescribed. Upon receiving the search message s, with the processingmeans N3 a, the node N3 reads the identifier N1 of themalfunction-related node from the search message and compares theidentifier N1 with the data N3 stored in the self-node-ID storage N3 band the data N1, N2, and N10 stored in the adjacent-node-ID storage N3c. As a result of these comparisons, since the identifier N1 coincideswith the data N1 stored in the adjacent-node-ID storage N3 c, the nodeN3 sends a response message r to the node N2 so to establish analternative transmission line between the nodes N2 and N1, that is, toconnect the alternative transmission line CR2, the alternative maintransmission line CR, the alternative transmission line CR3, the nodeN3, the transmission line R3, and the transmission line R1 in thatorder, and also sends a route setting signal to its own route changesection, instructing for setting a bypass route to the node N2 via thenode N3 in place of the communication route to the node N2 via thetransmission line R2.

The response message r is a sending signal including information that amessage type is a response message, an identifier of the receiving nodeis N2, and an identifier of the sending node is N3, the informationbeing written in a control section of the corresponding signal frame.

Meanwhile, upon receiving the response message r, the node N2 readsinformation that the identifier of the sending communication device isN3; checks an opposing node to which a bypass route is to be set on thebasis of this information; and sends a route setting signal to its ownroute changing section, instructing for setting a bypass route to thenode N3 in a similar fashion to that in the above-mentioned embodiment.

(a-2) The setting of a bypass route via the node N13 will be described.

In a similar sequence to that described in the above-mentioned (a-1), abypass route connecting the alternative transmission line CR2, thealternative main transmission line CR, the alternative transmission lineCR13, the node N13, the transmission line R13, and the transmission lineR1 in that order is formed.

The bypass routes in accordance with the foregoing route setting signalsare set.

[Case (b)]

Another example case where the communication failure B1 occurs on thesignal transmission line R2 between the car controller 1 and the motorcontroller 2 and another communication failure B2 occurs on thealternative main transmission line CR will be described with referenceto FIGS. 2 and 3.

In this case, only the bypass route described in the above-mentioned(a-2) can be set, while the bypass route described in theabove-mentioned (a-1) cannot be set.

[Case (c)]

Another example case where the communication failure B1 occurs on thesignal transmission line R2 between the car controller 1 and the motorcontroller 2 and the communication failure B2 and another communicationfailure B3 occur on the alternative main transmission line CR will bedescribed with reference to FIGS. 2 and 3.

In this case, since there was no response to the polling in apredetermined time period, the node N2 detects the fact that the node N2has lost all transmission lines to the car controller 1 due to theoccurrences of the communication failures B1, B2, and B3, and hencechanges the mode of the motor controller 2 from a standby mode to a stopmode so as to stop the inverters 10 and 10′.

The car controller 1 detects the fact that there is no response from thenode N2 in a predetermined time period, disconnects the node N2 from thetransmission lines, and then controls the remaining motor controllers bybacking up them via the remaining nodes.

A bypass route between the car controller 1 and each of the controllers2, 3, 4, 5, 10, 11, 12, and 13 is set in a similar fashion to that inthe above mentioned embodiment.

As described above in detail, the present invention offers the followingadvantages.

(1) In an electric car of a type in which each drive wheel isindependently driven, employing an electronic control for improving itsrunning stability, having a wheel system suspended by a tandem wheelsuspension, and equipped with an in-wheel drive system in whichelectronically controlled motors are incorporated into all wheels, evenwhen a certain electronic control system malfunctions the car can keepsits control operation while maintaining its control functions by settinga bypass route.

(2) Since a fail safe mechanism is incorporated into an electroniccontrol system, a stable car control can be performed. Moreparticularly, in an electric car of a type in which each drive wheel isindependently driven, having a wheel system suspended by a tandem wheelsuspension and equipped with an in-wheel drive system in whichelectronically controlled motors are incorporated into all wheels, sincea control for improving the running stability of the car is employed, aload on each wheel can be reduced and a TRC or ABS equivalent controlcommensurate with the reduction in load can be performed, therebyleading to a reduced risk of slipping and the like and improving therunning stability. Also, since the electronic control system isconstructed such that an output torque value is directed to each motorafter the output torque values are adjusted so as to prevent a new yawmoment from acting on the vehicle when at least one pair of non-slippingwheels exist at each of the right and left of the vehicle, a 8-WD systemis achieved while preventing a yaw moment from occurring and a reliablerunning-stability control under slipping is achieved.

(3) Since a fail safe mechanism is incorporated into an electroniccontrol system, a stable car control can be performed. Moreparticularly, in an electric car of a type in which each drive wheel isindependently driven, having a wheel system suspended by a tandem wheelsuspension and equipped with an in-wheel drive system in whichelectronically controlled motors are incorporated into all wheels, acontrol for improving the running stability of the car is employed,thereby leading to a reduced risk of slipping and the like and improvingthe running stability. Also, since the electronic control system isconstructed such that an output torque value is directed to each motorafter the output torque value is adjusted in accordance with theslipping state of the corresponding slipping wheel when no pair ofnon-slipping wheels exist at each of the right and left of the vehicle,a TRC/ABS equivalent control is achieved without a member for operatinga pressure of a brake fluid, and also since the TRC/ABS equivalentcontrol operates under appropriate circumstances, a reliablerunning-stability control under slipping is achieved.

INDUSTRIAL APPLICABILITY

Since a control device of an electric car according to the presentinvention performs an accurate control between controllers fixed tocorresponding electric motors, it is especially suitable as a controldevice of that which does not emit an exhaust gas affecting on globalwarming.

1. A control device of an electric car, comprising fail safe means forsignal transmission lines, wherein a bypass route is established suchthat a node detecting a communication failure in an electronic controlsystem of the car sends a search message for searching a transmissionroute and another node which is able to establish the transmission routesends back a response message, and wherein each of the nodes comprisesself-node-ID storing means for storing its own node identifier,adjacent-node-ID storing means for storing identifiers of adjacent nodesconnected to the transmission route, and processing means for processingroute setting on the basis of a message sent to the node.
 2. The controldevice of an electric car according to claim 1, wherein the node isprovided at each of a car controller and motor controllers, eachprovided at a pair of wheels.
 3. The control device of an electric caraccording to claim 2, wherein the bypass route is established by acontrol-signal-use, alternative main transmission line forming a closedloop and two alternative transmission lines connecting the alternativemain transmission line and two of the motor controllers.
 4. The controldevice of an electric car according to claim 3, wherein, when a certainnode detects that all communication lines and bypass routes to the carcontroller malfunction, the node stops an operation of the correspondingmotor controller, and the car controller detects that there is noresponse from the certain node and separates the motor controller of thecertain node from its control objects.
 5. The control device of anelectric car according to claim 1, wherein the node is provided at eachof a battery controller, a steering controller, a brake controller, anda battery charging controller.
 6. The control device of an electric caraccording to claim 5, wherein the bypass route is established by acontrol-signal-use, alternative main transmission line forming a closedloop and two alternative transmission lines connecting the alternativemain transmission line and two of the motor controllers.
 7. The controldevice of an electric car according to claim 6, wherein, when a certainnode detects that all communication lines and bypass routes to the carcontroller malfunction, the node stops an operation of the correspondingmotor controller, and the car controller detects that thee is noresponse from the certain node and separates the motor controller of thecertain node from its control objects.
 8. The control device of anelectric car according to claim 1, wherein the car controller and themotor controllers, each provided at a pair of wheels, controlcorresponding power converters in accordance with control signalsreceived via the corresponding nodes.